Engine misfires at low speeds

OK – thought I might be able to trouble shoot this by reading all the other threads I could find on it, but I am not sure my problem fits exactly with the others I've looked at.

I recently purchased a 2002 EGlide EFI (FLHTCI). The bike has V&H oval slip-ons, K&N breather and stage 1 download. It has 14K on it and was running near normal when I bought it a few weeks ago. I had the local HD dealer perform a 15K service and they thought everything looked good/ran fine. It had decel popping that prior owner told me about – he thought the fuel mapping was off (has RevTech DFO), but dealership told him they had “optimized” it. However, since I bought it the engine is not running well at low speeds. It basically runs fine under mild/strong acceleration or at full highway speed and seems to idle normally when the bike is started. However, when cruising along about 25-30 mph (in either 2nd or 3rd gear) it is always misfiring and sputtering pretty bad now (had a little hint originally and definitely getting worse now). After coming to a stop, the idle is a bit rough and sometimes the engine acts like it wants to cut out for a few seconds after which it seems to idle OK. The popping/backfire also continues about the same on decel as when I got it. The symptoms appear to be about the same whether the bike is cold or warmed up. I was thinking it might be bad gas (last owner did not ride it last year). I have put 3 tanks of 93 octane through it and no change (and no difference between full or near empty full tank). I also consulted with RevTech and tried adjusting the DFO pot settings which seemed to be way off from what they should be for my set up, but I can’t notice much change across fairly large adjustments. RevTech thought it was likely an intake leak, but before I start making a mess with WD40 to check it out, wanted to get some feedback. It seems like an intake leak would make the bike run rough at idle too. I have pulled the diagnostic code from the data link and on the tables I pulled off this forum I am getting a 34 which is listed either as loss of idle speed/air control and/or starter output high. I had squirted a little carb cleaner into the air intake which caused a quick loss in rpm so maybe that caused the trouble code – not sure.

Any suggestions on what problem I should be going after or how to verify?

It could be many things but go with the simplest first, run it till warm and then spray the intake to head area to eliminate that area as a problem. If there is no change in the engine rpm then it may be dirty injectors in which case a little injector cleaner won't hurt or you could use some Marvel Mystery Oil in the fuel, none of which will harm the bike and may even fix your problem at a very small cost. Also, can you actually notice a difference when you change the settings on the fuel manager? I have a TFI on my bike and have found through this forum it seems to be the best one out there and Dobeck is here to help and they really do.

However, when cruising along about 25-30 mph (in either 2nd or 3rd gear) it is always misfiring and sputtering pretty bad now (had a little hint originally and definitely getting worse now).

Click to expand...

Draggin is correct, it can be 1 of many things. But before I went crazy digging in deep, the first thing I would check is fuel pump pressure. With that age bike, having a mid range steady cruise engine miss, I would have to know what the fuel pressure was before going any further. Unfortunately, unless you have the right tool, it is not easy to test it.

Thanks guys - got a couple things to look at. A while back when I first read the about the pin hole problem, I thought it went away with a full tank (mine does not go away). After rereading it I understand that it may or may not get better with a full tank. Will try to check this first and then maybe go to the intake leak test. After that, might need to take it to the dealer as I dont have many diagnostic tools.

Update - I opened the gas cap and listened/watched while the pump pressures up. It doesn't seem to take too long and I can't hear or see anything abnormal (hissing, bubbling, spraying, etc.). At only 14K on bike, seems like it shouldn't rub through that quick anyway.

Next, I tested both WD40 and my carb cleaner into the throttle valve. The carb cleaner got the best response (just a little stalled the bike). I then started the bike and sprayed some around top and bottom of both front and rear intake manifold where it mates to the cylinder head. No response at all so I assume the intake is not leaking. I hadn't looked at the spark plugs so I pulled both. There is a difference - the front plug is black on top and the insulator is a little dark (plug doesn't really look fouled, just dark). The rear plug is a tan/white color on top and the insulator is white (maybe running hot?). What might this be telling me - dirty rear injector?

I tried to upload a picture of the plugs (first time trying, so it works).
Pic should be better than my description.

Without tools it is hard to diagnose the problem. May want to try this.
Get the tank fuel level to about 1 gallon so the holes (if any) will be above the gas level. Remove the fuel pump relay and jumper pin 87 to pin 30 (look at relay bottom) at the harness socket. Leave relay removed. With the engine off, turn ignition to on. The pump will run continuous and not just for a 2 second prime.
Check inside tank for spray or leaks

Hoople ... sorry if I wasn't clear. I was trying to say that I have the problem when the tank is near empty and the same problem when the tank is topped off full. Basically the sputtering at low rpm/speed is always there, but has gotten a bit worse over the few weeks since I bought the bike. I will try the check you describe.
(do you think the different plug color points to anything?)

Thanks guys - got a couple things to look at. A while back when I first read the about the pin hole problem, I thought it went away with a full tank (mine does not go away). After rereading it I understand that it may or may not get better with a full tank. Will try to check this first and then maybe go to the intake leak test. After that, might need to take it to the dealer as I dont have many diagnostic tools.

Update - I opened the gas cap and listened/watched while the pump pressures up. It doesn't seem to take too long and I can't hear or see anything abnormal (hissing, bubbling, spraying, etc.). At only 14K on bike, seems like it shouldn't rub through that quick anyway.

Next, I tested both WD40 and my carb cleaner into the throttle valve. The carb cleaner got the best response (just a little stalled the bike). I then started the bike and sprayed some around top and bottom of both front and rear intake manifold where it mates to the cylinder head. No response at all so I assume the intake is not leaking. I hadn't looked at the spark plugs so I pulled both. There is a difference - the front plug is black on top and the insulator is a little dark (plug doesn't really look fouled, just dark). The rear plug is a tan/white color on top and the insulator is white (maybe running hot?). What might this be telling me - dirty rear injector?

Have tried a few more things:
Got the tank down to about a half gallon so that pin holes (if present) would be above fuel line - hard to see into my tank, but checking with light and also putting ear down to opening, I can't pick up on anything unusual indicating a spraying or leak.

Checked compression (engine just warm to touch) and measured 130 psi on front and almost 135 on rear so pretty well balanced, but is this too low?

Changed the spark plugs just to see if it would affect the problem - found no difference.

I have noted exhaust smelled rich when sitting at stop light or idling and also poor gas mileage (I haven't gotten any more than 36 mpg even with mostly highway riding). On the outside chance my DFO was adding more fuel than it should, I unplugged it and ran the bike about 5 miles. All I could notice was that my idle speed dropped about 200 rpm, but misfiring was just as bad.

A couple other comments - cruising between 2000-2500 rpm (really about any gear), the motor acts like it is running on one cylinder. As I get up to about 3000 it is running nearly the way it should. Also, the problem is a little worse when the motor is warmed up ... once it is up to temperature, it bucks sometimes when starting to accelerate slightly. When I roll throttle a little, the engine starts to cut out then picks up and accelerates smoothly with no indication of misfire or power loss.